From: "Daniel Kropveld (neufys)" To: Multiple recipients of list Subject: Idea: a very bright flasher The message below is written for the group rec.kites, but very inventive scouts leaders who are in for crazy ideas may find this simple to build device useful for all sorts of activities. It is a flasher which I use to lift off in my kites. It gives a UFO-ish effect. I have about a dozen of them, and I used them at a night activity of my scouts, hung them in trees every 200 meters to mark a trail which the scouts had to follow. They were told to follow a trail, but it was not told which kind of signs they had to follow. It was a big succes! Last weekend I also played a fox-hunt during a dark night with a flasher mounted on a cap. Certainly you may find other uses for these flashers! Do your best! Daniel Kropveld, Phoenix group, Amsterdam. NL. <|:-)>= --------------rec.kites message follows below ---------- A *very* bright flasher! For quite some time now I have been experimenting with different kinds of flashers: some time ago I wrote a short message on this list about my very bright flashers, and since then I have been receiving many questions about the details. So here the full story for the ones who requested it, and to the list in general: My experience is that LEDs do not give enough light. I have tried to add more LEDs in parallel, but with little succes. So I tried to use bulbs, the plain ones that can be found in simple torches. The more voltage you apply to a bulb, the brighter it lights up. For instance, when you apply 6 Volts to a bulb which is rated for 2.5 Volts, it emits light as bright as a photographic flasher. And that is what we want. The only problem is that the bulb is dead before you could even lift off your kite 8^(. The reason for burning the bulb is that with such an overrated voltage, the heat which is developed inside the bulb melts the glowing wire inside. So what you do is not to allow the bulb to develop so much heat, and in this case I solved this to minimize the time that the bulb glows up, and then allow much time to let the bulb cool off. Let's go practical: I used the LM3909 LED Flasher/Oscillator (National Semiconductor) to time the flashing. (The same timer which is used in the LED flashers described before on this list.) The bulbs light up about once a second, and for a duration of estimated 0.1 seconds. This short time is long enough to make the bulb light up fully, but just too short to burn it. After one night of use you will note a dark coating on the inside of the bulb, which is caused by vaporizing of the glowing wire inside. It is advisable to have some extra bulbs handy, because some do not last a full night. As you can see on the schematics below, there are only 3 parts. The bulb is rated at 2.5 Volts, and can be found on torches that run on a single battery. (They can also be found in shops 8^). Do not use these halogen type bulbs. The batteries are 4 cells of 1.5 Volts. The current used is little, so you can use the smallest batteries (AA) you can find, if you need to save weight. Solder the batteries together, and fix them well to your kite. They behave like bombs if they jump out of a container up in the sky! Also fix the bulb with a piece of tape, so that it does not come loose up in the sky. On the diagram the LM3909 is drawn top view, a little dot on the housing denotes pin number 1. The electrolytic capacitor is 400 - 500 microfarad, 10 Volts; note the polarity. The cost of one unit is about 10 guilders ($5). Note that when a bulb of a different voltage is used, the timing changes considerably. Also, to increase the flashing speed by a factor of about 2, connect pin 8 with pin 1. This ofcourse will decrease the life-time of the bulb. The diagram: ----------------------------------------- | -------- | | | | | | | | | ++0++++0++++0++++0++ | | | + 8 7 6 5 + |+6 Volt | | + + ------------- X L | ) LM 3909 + ===== | | + + | | | +.1 2 3 4 + | | | ++0++++0++++0++++0++ | | | | | | | | | -------------- | -----||-----| | C + | | | ------------------ Legend: */\* *\/* |+ | \ ------------- X L Lightbulb, 2.5 volts ===== Battery | \ | \ --||-- Electrolytic Capacitor, 470 microF C + note the polarity! \ \ This little device competes very well with the expensive and heavy photographic (Xenon-) flashers. But you can improve the intensity by adding a reflector. The one I use is taken out of my son's torch (he had no use of a torch without a bulb anyway :-). Remember to direct the reflected light beam down. \ \ Good Luck, \ Daniel Kropveld, Amsterdam \ o \8/ KROPVELD@AMC.UVA.NL ^